tunnel: retry DNS resolution for 10 seconds

This has several problems: 1) it blocks the main thread; 2) it doesn't
distinguish between a permanent error and a transient one; 3) the 10
seconds is hard coded; 4) there's no way for the user to cancel it.

We'll have to improve this.

Signed-off-by: Jason A. Donenfeld <Jason@zx2c4.com>

ui/src/main/java/com/wireguard/android/util/ErrorMessages.kt

@@ -36,7 +36,8 @@ object ErrorMessages {
             BackendException.Reason.VPN_NOT_AUTHORIZED to R.string.vpn_not_authorized_error,
             BackendException.Reason.UNABLE_TO_START_VPN to R.string.vpn_start_error,
             BackendException.Reason.TUN_CREATION_ERROR to R.string.tun_create_error,
-            BackendException.Reason.GO_ACTIVATION_ERROR_CODE to R.string.tunnel_on_error
+            BackendException.Reason.GO_ACTIVATION_ERROR_CODE to R.string.tunnel_on_error,
+            BackendException.Reason.DNS_RESOLUTION_FAILURE to R.string.tunnel_dns_failure
     )
     private val KFE_FORMAT_MAP = mapOf(
             Key.Format.BASE64 to R.string.key_length_explanation_base64,

ui/src/main/res/values/strings.xml

@@ -214,6 +214,7 @@
     <string name="tunnel_list_placeholder">Add a tunnel using the blue button</string>
     <string name="tunnel_name">Tunnel Name</string>
     <string name="tunnel_on_error">Unable to turn tunnel on (wgTurnOn returned %d)</string>
+    <string name="tunnel_dns_failure">Unable to resolve DNS hostname: “%s”</string>
     <string name="tunnel_rename_error">Unable to rename tunnel: %s</string>
     <string name="tunnel_rename_success">Successfully renamed tunnel to “%s”</string>
     <string name="type_name_go_userspace">Go userspace</string>